Posted on 03/13/2002 4:47:26 AM PST by JediGirl
No. Recent molecular phylogenetics supports the multiple origin hypothesis. Note that each hypothesis, multiple or single-origin, comes with a difficulty. Either eyes evolved independently multiple times or else they were lost multiple times.
Sorry. Didn't mean to interrupt. You're doing great.
Eyes often take a central role in discussions of evolution, with debate focused on how often such complex organs might have evolved. One such debate is whether arthropod compound eyes are the product of single or multiple origins. Here we use molecular phylogeny to address this long-standing debate and find results favoring the multiple-origins hypothesis. Our analyses of DNA sequences encoding rRNA unequivocally indicate that myodocopidsthe only Ostracoda (Crustacea) with compound eyesare nested phylogenetically within several groups that lack compound eyes. With our well-supported phylogeny, standard maximum likelihood (ML) character reconstruction methods significantly reconstruct ancestral ostracods as lacking compound eyes. We also introduce a likelihood sensitivity analysis, and show that the single-origin hypothesis is not significantly favored unless we assume a highly asymmetric model of evolution (one favoring eye loss more than 30:1 over gain). These results illustrate exactly why arthropod compound eye evolution has remained controversial, because one of two seemingly very unlikely evolutionary histories must be true. Either compound eyes with detailed similarities evolved multiple times in different arthropod groups or compound eyes have been lost in a seemingly inordinate number of arthropod lineages.
I misunderstood your earlier question. Once "invented" (your term) such a feature could be inherited by the posterity of the creature possessing such a mutation. I thought you were asking if mammary glands could also appear elsewhere on the tree, thus my response about the raw material which gave rise to the original mutation. If it still exists in the "parent" stock, I suppose the same (or perhaps similar) mutation could pop up again, in a new branch (thus my platypus comment). As you say, this seems to happen with eyes.
OK. I don't like "multiple loss" in something that would obviously be very valuable. I can see why they made the call the way they did.
You have a certain flair, quite unlike your creationist bretheren. Don't let VadeRetro beat up on you too much, you're much more fun than our other opposition.
If something exists in your parents, you may well just inherit it. It doesn't have to pop up again, it never went away.
Here's where gore and some others confuse people by trying to say that the platypus doesn't fit the tree. It does. It's a mammal. It comes away from our branch even before the invention of the marsupial pouch, but it's a mammal.
It inherited the mammary glands from the common ancestor of modern mammals.
But why didn't T. rex inherit mammary glands from anybody?
One might say it's closer to being the mammal "trunk" than our branch. IOW, it's a "primitive" mammal, a clue to our origins. (But it's been evolving as long as we have.)
I know that. I was making a different point about the persistence in the parent stock of the genetic raw material which was amenable to the mutation.
But why didn't T. rex inherit mammary glands from anybody?
I assume this rather silly question is one which stumped g3k and the other creationists. In the evolution model, I suppose it's because the mutation for such a feature hadn't yet appeared. In the "simultaneous creation of all species" model (to which I don't subscribe) such a mutation would most definitely have appeared at the same time as everything else, yet it would have been present only in those creatures upon whom it had been bestowed, and thus it would be "locked in" to them, as it were. In a "gradual creation of all species" model (my favorite) you get pretty much the same thinking. Mammary glands exist where they've been created. To the evolutionist, take the last sentence and substitute "when" for "where." Same result.
It appears as if that "random" bugaboo has someone flummoxed again.
You have trouble staying in evo mode for long, but I think you're there. The new features can only inherit up the tree. There's no jumping branches or going down.
The ancestors of mammals, Synapsida, branch off that Amniote tree I linked earliest of all. The lineage they left behind does a bunch of branchings thereafter, giving rise eventually to the diapsids, which include dinos and their bird descendants.
T. rex having mammaries would be a case of inheriting from a fifteenth cousin, or more like the future descendants of a fifteenth cousin. Unless T. rexes invented their own which were lost when T. rex died out. An unlikely happening with no evidence.
". . . branch earliest of all off of that tree . . ." Tired.
Forgot to mention that we could move the invention of mammaries back to some common ancestor of T. rex and the synapsids, then figure out some loopy reason no other descendants have the milk glands. (Nah!)
This is not a terribly complicated point. If I didn't address it directly the first time you hinted at it, I guess it's because I was looking for greater subtleties. I'm well aware, as are most creationists, that our ancestors don't inherit from us. (I find it incredible that you think it necessary to expound upon that point.) Indeed, as I think I've demonstrated, I have a fair understanding of evolution, at least in its broad outlines. And although a creationist, I'm not insane or incapable of reason. I do not consider evolutionists to be a gang of fraudulent con artists, and I'm very distressed at the tactics of many other creationists in these threads. I regard evolution as a provisional hypothesis. I don't even get upset when it's taught exclusively in the schools. I think you've taken an unnnecessarily hostile approach in my case, but that's okay. You don't know me.
That's fine. I shall now return to lurking mode. But as they say ... I'll be back.
Didn't mean to seem that way. I was sincerely trying to guide you to the point, which is that the common descent hypothesis lets you reason unattested properties of animals for which you know something about ancestors and descendants. I don't feel any hostility to you at all. On the contrary, your attitude on these threads has proven exemplary.
Perhaps, from all the questions, you thought I had you in what I've come to call "tallhappy mode." An unfortunate precedent was set by the way that person used the quiz show as a bludgeon.
Don't take it personally, No-Kin. If you only knew what ol' Vade's had to contend with in these threads, you'd better understand that he approaches each new creationist in an already-frustrated mood. And in virtually every case, it's justified.
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